Earth and Space

Pickering’s female stars

Stories from Physics for 11-14 14-16 IOP RESOURCES

The astronomer Edward C Pickering was director of the Harvard College Observatory for 43 years from 1877. He made significant contributions to astronomical photography and categorisation. However, what is most remarkable is that his team of researchers included an impressive array of women, exceptional for that time. However, whilst Pickering was progressive in encouraging women to contribute to research, the female members of his team were typically paid half the salary of their male colleagues.

Fleming’s fantastic findings

One of the most well-known images of a nebula - the horsehead nebula - was captured on a photographic plate in 1888 by Williamina Fleming at Harvard Observatory. Fleming’s story is remarkable: after immigrating to the United States from Scotland, she became pregnant only to be deserted by her husband. She came to work for Pickering, at first as a maid. One day, Pickering became so annoyed with the slow progress achieved by his male assistants that he stormed out of the building in a huff claiming that his Scottish maid could do a better job. This story may have been embellished in the retelling but, nevertheless, Fleming began to work with Pickering and went on to publish papers in prestigious astrophysical journals. She became an honorary member of the Royal Society which did not allow women as regular members at the time. Among Fleming’s many achievements are the discovery of ten novae, over 300 variable stars and the first recorded spectrum of a meteor.

Jump Cannon’s classification

One of the earliest systems of star categorisation, the Harvard system, was developed by Pickering and his team in 1890. One member of the group, Annie Jump Cannon, was a remarkable astrophysicist. As a child, she would conduct observations with her mother from an impromptu observatory built in the attic of the family home. During her youth, perhaps due to a bout of scarlet fever, Jump Cannon suffered severe hearing loss. Encouraged by her parents to study physics at Wellesley College, Jump Cannon did not pursue her interest in astronomy for ten years after her graduation. Biographers have suggested that the death of her mother acted as the spur to restart her scientific career and she found a post at the Harvard College Observatory. Whilst working for Pickering, she developed an extraordinary ability to classify stars, being able to categorise the spectra of three stars per minute. She increased the star card catalogue from 14,000 entries to some 250,000.

Jump Cannon developed Pickering’s classification system into one that ranked stars by their temperature into groups labelled O, B, A, F, G, K and M. A story was told at the observatory that Jump Cannon could remember every serial number of every photographic plate she had analysed – if true, a remarkable feat given she classified over a quarter of a million plates.

Pickering described her contribution to astronomy as “a structure that probably will never be duplicated in kind or extent by a single individual”. Her peer, Cecilia Payne-Gaposchkin (see page 13), described Jump Cannon as the happiest person she had known. Though Jump Cannon had no children herself, she would hold parties for young people at her home in the Observatory estate, Star Cottage.

Leavitt’s pulsing stars

Henrietta Swan Leavitt worked for Pickering and, like Jump Cannon, had a hearing impairment. At this time, women were typically not allowed to operate telescopes so she worked cataloguing and comparing photographic plates of stars. PayneGaposchkin argued that not allowing Leavitt to use telescopes “was a harsh decision, which condemned a brilliant scientist to uncongenial work, and probably set back the study of variable stars for several decades”.

Leavitt made an important discovery about the relationship between the period of pulsation and luminosity of Cepheid variable stars, providing a ‘standard candle’ for astronomers to use to measure distances.

In addition, she discovered some 2,400 variable stars, around half the catalogue of such objects known in 1930. Leavitt died before the significance of the periodluminosity relationship she discovered was fully appreciated but Hubble claimed her research should have won the Nobel Prize.



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